Lightning Studies Based on Measurements Spanning the Ranges from Radio Frequency to Optical (including Infrared and Ultraviolet) to Gamma-Rays

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Lightning is a spectacular natural phenomenon but also a severe hazard to human life and property. A number of fundamental questions on how lightning actually works are still open and cannot be answered without the use of nontraditional approaches and tools. Optical observations of lightning in an unprecedentedly wide wavelength range using a unique array of high-speed framing cameras operating, besides the traditional visible-range, also in the medium-to-far infrared (IR) and near ultraviolet (UV) ranges will be performed to get a view of lightning processes that has never been possible before. IR images will provide a measure of temperature in different parts of the lightning channel and UV images will make it possible to detect “cold” lightning processes (such as corona streamer bursts) which play a fundamental role in determining lightning behavior. Observations will be carried out at the Lightning Observatory in Gainesville (LOG), Florida, in conjunction with recordings of corresponding radio-frequency electromagnetic field and penetrating radiation (x-rays and gamma-rays) signatures. The anticipated results will potentially impact an unusually large number of areas/disciplines, including, besides the lightning physics, (1) the global electric circuit, in which corona is one of the key processes that keep the Earth negatively charged, (2) cloud electrification (corona at ground may be a significant contributor to the formation of the lower positive charge region), (3) high-energy atmospheric physics (corona streamer bursts produce x- and gamma-rays), (4) lightning protection (corona-emitting systems sometimes are claimed to control the lightning termination point), and (5) thunderstorm warning (occurrence of corona is an indicator of thunderstorm hazard).The project is aimed at answering the following new science questions: (1) What is the role of corona streamers in the various phenomena associated with thunderstorms and lightning? (2) What can we learn from direct comparison of high-speed recordings of lightning in the IR, visible, and UV ranges? (3) What processes (besides the attachment process) create loops in the lightning channel? (4) How fundamental are the differences between +CGs and –CGs? Observations with the new UV camera will first target the streamer zone of descending leader branches and that of upward unconnected leaders. Then, the possibility of imaging the common streamer zone formed during the lightning attachment process and the lightning channel corona sheath will be explored. IR images will allow clear imaging of the evolution of the early stage of return-stroke process, which is impossible in the visible range due to significant light scattering. Also, IR images will be used to distinguish between parts of the leader channel network that are at different stages of their heating and cooling processes, while UV images will show essentially cold (and generally undetectable in the visible range) streamer formations. Synergistic results will be obtained from simultaneous observations in this unprecedentedly wide optical wavelength range, which will be performed in conjunction with the corresponding recordings of RF electromagnetic field signatures and energetic radiation. Further, the recently observed mysterious loops in the lightning channel will be examined and conditions under which +CGs exhibit features characteristic of –CGs will be identified.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.